In general, a vehicle manufacturing process combines various structural components, including a welding process of pressed formed vehicle body panels, and finishing process of painting a surface of the vehicle body.
Then, in a fitting process, power train system components and components of systems, such as a suspension system, a steering system, a braking system are assembled, and then, doors, a trunk lid, a hood, and so on are assembled.
In combining vehicle body components, such as a roof, pillars, side panels, flanges for opening of the doors, and so on in a vehicle body assembly process, resistance spot welding is used for combining two vehicle body panels by using a spot welding apparatus.
In the resistance spot welding, the two vehicle body panels are welded by electrical resistance while applying a pressure to surfaces of the two vehicle body panels, in general, by using the spot welding apparatus mounted to front ends of welding robot arms.
The spot welding apparatus has one set of spot welding unit with an X-type welding gun, a C-type welding gun, or a special type welding gun selectively applied thereto depending on whether a position of a welding portion interferes with the vehicle body or not mounted to the robot arms.
Consequently, the spot welding is carried out with a plurality of robots provided on a line, including a robot having the spot welding unit with the X-type welding gun applied thereto, a robot having the spot welding unit with the C-type welding gun applied thereto, and a robot having the spot welding unit with the special type welding gun applied thereto.
However, the related art spot welding has drawbacks in that much time period is required for carrying out the required number of welds, and productivity and efficiency are poor because one set of the spot welding unit is mounted to the robot arms of every one set of the robot, enabling to make one point of welding every moment the robot arm move.
Moreover, the related art spot welding requires a lower welding gun of shapes varied with positions and shapes of welding points to increase an equipment investment expenditure, and particularly, since the plurality of robots each having the spot welding unit with the lower welding gun of the special shape applied thereto is required, the related art welding has drawbacks in that equipment and maintenance cost increases, energy is used excessively, and an occupation ratio of the robots increases.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.